The present invention relates generally to a torsional vibration damping device used generally in a flywheel assembly. More particularly, the present invention relates to a viscous torsional vibration damping device having variable dampening means responsive to relative rotary displacement of a first flywheel of a flywheel assembly and an output rotation member which are connected to each other for limited rotary displacement.
A viscous torsional vibration damping device damps torsional vibration utilizing a resistance force produced when viscous fluid passes through a choke or the like, and is used, for example, in a flywheel between the engine of an automobile and a clutch disc assembly. When a viscous torsional vibration damping device is used in a flywheel, the flywheel is typically divided into two flywheels, and the viscous torsional vibration damping device is disposed between the two flywheels.
In a viscous torsional vibration damping device, it is desirable to vary the resistance force caused by the passage of viscous fluid in the dampening device in response to the operating conditions so as to effectively damp the torsional vibration in a wide operating regions. A small resistance force is desirable in damping small torsional vibration such as the vibrations associated with idling of an internal combustion engine. A large resistance force is effective in damping low-frequency vibration caused by rapidly pressing down the accelerator or releasing the accelerator quickly. Therefore, a conventional viscous torsional vibration damping device include a first damping part for producing a small resistance force in a range of small displacement angle between the first flywheel and the second flywheel and a second damping part for producing a large resistance force in a range of large displacement angle therebetween.
In the above described torsional vibration damping device, there are two levels of damping resistance force. The resistance force in the first damping part is small so as to absorb vibration at the time of idling, for example. On the other hand, the resistance force in the second damping part is large so as to considerably absorb the low-frequency vibration. However, when vibrations in the flywheel system are such that the relative displacement of the two displaceable parts causes fluctuates between the two levels of resistance force, the fluctuations produce a shock, thus limiting the effectiveness of the damping device.